In his top-down view of the center of our solar system, you can see how many asteroids we've been able to spy since 1970.

The sun is in the middle of the animation, with Mercury, Venus, Earth, Mars, and Jupiter swooping around it. The green flecks represent asteroids we've discovered swirling in the asteroid belt, the main river of rocks that whirl around the sun between the orbits of Mars and Jupiter:

The yellow flecks are asteroids that have inched closer, crossing into the orbit of Mars. And the red dots are the most menacing of all: the asteroids that drift into the orbit of Earth.

Take a look at the number of asteroids we knew about in 1970 — just a few thousand. The numbers at the bottom left of the animation show the year and the number of asteroids we knew about at that time.

By the 1980s, as Manley says in one of his older videos, astronomers used photographic plates to collect and record their observations. This essentially involved printing a photographic negative onto a glass plate.

But you can see that by the mid-1990s, when astronomers switched to collecting and storing its images electronically, the number of asteroids we could detect exploded. This is because we could detect, process, and analyze images much faster than we could with photographic plates.

By the late 90s, many dedicated asteroid discovery programs were in full swing, according to Manley, driving up the discovery rate to hundreds per day.

Then, with the huge help of WISE — NASA's wide-field infrared survey explorer, a space telescope that scans the entire night sky using infrared — we've detected more than half a million asteroids.

While it may seem scary to be surrounded by all of these asteroids, the distances aren't as close as they seem. One pixel at the highest resolution is equivalent to a distance of about 311,000 miles.

But there's one sobering fact to all of this: We've only discovered a fraction of the total number of asteroids that are swirling about our solar system.

For this reason, we're constantly detecting, tracking, and monitoring these near-Earth objects (NEOs), as they're called, with both ground-based and space-based telescopes. And it's incredible how much technology has advanced over the past 45 years to allow us to see more than we ever could have imagined.

NASA is currently tasked with finding 90% of NEOs that are just slightly bigger than a football field — 450 feet or larger — by the end of 2020. So far, the space agency estimates it has detected only about 25% of them.

That's why the government recently set up a brand-new office, called the Planetary Defense Coordination Office, to identify and deflect potentially devastating asteroid strikes before it's too late.

But NASA isn't the only agency in the asteroid hunting game. If all goes as planned, the privately-funded B612 Foundation will launch the first dedicated asteroid-hunting telescope into space by 2018. If successful, the Sentinel space telescope will find more than half a million objects circling dangerously close to Earth, giving us time to plan a deflecting strategy should one pose a serious threat.

Check out Manley's entire video on the mind-boggling numbers of asteroids we've found here: